The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
A vehicle may include an engine and an exhaust system having a lean NOx trap (LNT) catalyst with a plurality of channels through which engine exhaust passes. Surfaces of the channels may be impregnated, for example, with barium salts and platinum or other precious metals. During lean operation of the vehicle engine (an air-to-fuel ratio greater than 14.7), the catalyst may adsorb oxides of nitrogen (NOx) from the engine exhaust. The nitrogen oxides (typically NO and NO2) may be stored on the catalyst surface. The catalyst may periodically be exposed to a rich fuel environment (an air-to-fuel ratio less than 14.7), during which the catalyst may be converted (or regenerated), i.e., the stored NOx is reduced. Specifically, the nitrogen oxides may be converted to nitrogen, carbon dioxide and water in the presence of heat, carbon monoxide and hydrocarbons in the exhaust stream.
LNT catalysts may effectively store NOx at temperatures lower than temperatures at which they can effectively reduce the stored NOx. At low temperatures, for example, at temperatures less than about 300° C., a LNT catalyst may store NOx for a limited time, i.e., until it becomes full of NOx, or saturated. The saturated catalyst may be heated to a temperature exceeding the low range, and the heated catalyst may undergo regeneration.